In document WO 2005/090736, a motorized winding device is described equipped with damping flexible elements allowing a certain vibrational uncoupling between the motor assembly and its environment, so as to minimize the vibrations and noise perceived by the user. It is thus proposed to insert a rotary damping flexible element between the output shaft of the motor assembly and a winding drum of the screen. It is also proposed to insert a stationary damping flexible element between the casing of the motor assembly and a stationary support.
Under some circumstances, the insertion of a damping flexible element, whether rotary or stationary, may create uncertainty regarding the angular positioning of the drum driven by the motor, for example due to creep of the damping flexible element, or a variation in the static load torque.
Independently of the potential presence of damping flexible elements, similar phenomena may be encountered due to the aging of certain components of the actuator, for example in a reduction stage inserted between the motor and the drum. Other drifts may be related to differential thermal expansions of the components of the actuator.
When a rotation sensor connected to the motor is used, in particular a rotation sensor of the rotor, or rotary part, of the motor, to detect certain remarkable positions of the screen, and in particular end-of-travel positions, the aforementioned uncertainty may create imprecision in the control of the apparatus, for example resulting in incorrect positioning of the screen at the end of travel. Precise positioning is indeed required in particular for sun protection screens on a façade, since they must keep load bars perfectly aligned in extreme or intermediate positions.
A specific sensor may naturally be used, for example positioned between the drum of the screen and the stationary support, to precisely measure the angular position of the drum in a fixed frame of reference. However, the cost of such an additional instrumentation of the device is high if one wishes to obtain a satisfactory precision level of approximately +/−3 to 5°. Indeed, the rotation speed of the drum being considerably lower than the output speed of the motor, it is necessary to provide a much higher angular positioning precision.
There is therefore a need to improve the control of a motorized winding device of the aforementioned type, so as to decrease positioning errors, using simple, robust and inexpensive means.